Generally, vascular access devices are used for communicating fluid with the vascular system of patients. For example, catheters are used for infusing fluid, such as normal saline solution, various medicaments, and total parenteral nutrition, into a patient, withdrawing blood from a patient, or monitoring various parameters of the patient's vascular system.
A common type of intravenous (IV) catheter is an over-the-needle peripheral IV catheter. As its name implies, an over-the-needle catheter is mounted over an introducer needle having a sharp distal tip. At least the inner surface of the distal portion of the catheter tightly engages the outer surface of the needle to prevent peelback of the catheter and thus facilitate insertion of the catheter into the blood vessel. The catheter and the introducer needle are assembled so that the distal tip of the introducer needle extends beyond the distal tip of the catheter with the bevel of the needle facing up away from the patient's skin. The catheter material can be partially transparent and can have stripes of transparent material and opaque stripes for providing x-ray contrast. The catheter and introducer needle are generally inserted at a shallow angle through the patient's skin into a blood vessel.
In order to verify proper placement of the needle and catheter in the blood vessel, the clinician generally looks for blood flashback as confirmation of the access. The first blood flashback is through the needle and into a transparent needle hub, which is sometimes referred to as primary blood flashback. This confirms at least the needle has found the vein. Then as the needle is withdrawn in a proximal direction away from the catheter tube, the blood will flash back between the needle and the catheter tube. This is sometimes referred to as secondary flashback, which confirms that the catheter tube has found the vein. Once proper placement of the catheter into the blood vessel is confirmed, the clinician may apply pressure to the blood vessel by pressing down on the patient's skin over the blood vessel distal of the introducer needle and the catheter. This finger pressure occludes the vessel, minimizing further blood flow through the catheter and possibly leaking out the catheter hub.
In some IV catheter assemblies, the needle has an open notch, through which blood can flow into the space between the needle and catheter. This “instant flash” confirms only that the needle tip has entered the vein but not necessarily that the catheter tube has entered the vein. Because there is first blood between the needle and the catheter tube when a notch is employed, a secondary flashback is not possible.
The clinician may then withdraw the introducer needle from the catheter. The introducer needle may be withdrawn into a needle tip shield or needle cap that covers the needle tip and prevents accidental needle sticks. When the needle has an open notch, the blood between the distal opening and the open notch is not held by capillary action and can drip from the needle.
Blood dripping from the open end of the needle can occur when removing the needle from the patient or the catheter hub after primary blood flashback is detected.